On 08/04/2015 08:26 AM, Thierry Reding wrote:
... [ discussion of new fdtdec_get_addr_size() implementation]
So what this does is really fix parsing of address and size cells in the
general case, though it would still fail for values of #address-cells or
#size-cells bigger than 2 (because we don't have a datatype that would
be able to contain such large values).
Note that there's also still a corner case that this doesn't handle. The
DT specification states, if I remember correctly, that #address-cells
and #size-cells are inherited. That means with the current code we will
wrongly parse something like this:
/ {
...
#address-cells = <1>;
#size-cells = <1>;
...
bus@XXXXXXXX {
...
device@XXXXXXXX {
...
reg = <0xXXXXXXXX 0x1000>;
...
};
...
};
...
};
According to the DT specification the bus@XXXXXXXX node would inherit
#address-cells = <1> and #size-cells = <1> from the root node. However
with libfdt what really happens is that since bus@XXXXXXXX does not have
either property it will default to 2 in both cases. I'm not sure if this
really is a problem. Typically nodes are not nested that deeply, or if
they are then, typically, they explicitly contain #address-cells and
#size-cells properties.
I don't think #address-cells/#size-cells do actually get inherited.
Admittedly some other properties (e.g. interrupt-parent) do, but
according to:
https://lists.ozlabs.org/pipermail/linuxppc-dev/2008-January/049113.html
[PATCH] powerpc: #address-cells & #size-cells properties not inherited
... and my vague memory, these two don't.
You can search Google for e.g. "#address-cells inherited" and find a
number of similar assertions.
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